1) may have + done sth, can have + done sth

　　表示过去，推测过去时间里可能发生的事情。

　　Philip may have been hurt seriously in the car accident.

　　Philip can have been hurt seriously in the car accident.

　　2)　must have +done sth

　　对过去时间里可能发生的事情的推测，语气较强，具有肯定，谅必的意思。

　　---Linda has gone to work, but her bicycle is still here.

　　---She must have gone by bus.

　　3) ought to have done sth, should have done sth

　　本应该做某事，而事实上并没有做。否定句表示不该做某事而做了。

　　You ought to have been more careful in this experiment.

　　He ought not to have thrown the old clothes away.

　　ought to 在语气上比should 要强。

　　4) neednt have done sth　 本没必要做某事

　　I dressed very warmly for the trip, but I　neednt have done so. The weather was hot.

　　5) would like to have done sth　 本打算做某事

　　I would like to have read the article, but I was very busy then.